I'll list what I use and hopefully others can add suggestions to the mix.

For email and my address book, I use the Mozilla mail client, the latest incarnation of which is Thunderbird.

For calendaring, I use Yahoo! Calendar. It is very convenient since I can use it from anywhere when I'm traveling - all you need is a web access. I also really like how it will email out reminders before a given event. Email is one thing that I always check even while on the road, so I always get the reminders so long as I can find a way to get on the web (as I invariably do). Incidentally, if you sign up for a Yahoo! account, you'll also get access to Yahoo! Mail, which you can use to manage your contacts and email as well.

In that vein, other web-based solutions may provide a convenient alternative to Outlook as well and might be worth exploring.

Does that cover everything that you currently use Outlook for? If not, how else do you use it?

Brad, thanks for the pointer to Evolution. That's definitely something to consider if you want an Outlook alternative on Linux. Does it run on Windows too? I didn't see Windows mentioned on the download page and there is an Evolution for Windows website which said that the port is just for developers at this point.

nothingsmine, I just noticed that I left something out of my original response to your post. The alerts that Yahoo! Calendar sends will work even without web access or a computer (in the traditional sense), so it is even more convenient than I originally made it out to be. In addition to email alerts, you can also have the calendar send alerts to your mobile devices when an event is approaching. If the event is very important to me, I have it send a text message to my cell phone - that will always reach me, web access or not.

Sorry, I didn't know you were looking for cross-platform alternatives. AFAIK Evolution is strictly for Linux, although I'm happy to hear about the Evolution for Windows project...that will make migration easier for Windows users.

No problem. The alternatives don't necessarily need to be cross platform, so your suggestion was good. I just figured there is a good chance that the original poster is probably on Windows given that he is an Outlook user, but perhaps he is not on Windows and in any case listing non-Windows alternatives may help others reading this page.

Its in the very early stages of development but having used Outlook in a busy office enviroment myself I found the interface very fresh and clear and useful. I've been using it a while now and its never crashed. I even think theres a way to import your old events/tasks from outlook but havne't looked into it, you should give it a try.

thunderbird is the best (in my opinion) for POP3 and IMAP acounts.
for web email, go with excite, low storage space, but it is more compatible with firefox and macs than with windows. i do not recomend yahoo! or msn because they have recently turned over their email database to big brother bush. :(

I have been having problems with Microsoft Outlook for the longest, but I recently started college and since I have an email address with the school I obviously need some way to read the mail.
Thank you so much for the Thunderbird reccomendation. It was so easy to set up, and I got my mail in no time. I'm considering switching to Mozilla all together now. Thank you!

I've been using thunderbird for the past 2-3 months in managing 6-8 different POP3 accounts, it is just brilliant. The ease of use, the clean interface and the exclusion of unnecessary features (MS office cliche) makes it one of the best out there. The only thing I feel it lacks is the flagging feature frm outlook.. that came in handy for followup. It does have tags.. but the tag icons are too small to be significant.
Also if youre using thunderbird, try out thunderbrowse and minimize to tray add ons available on mozilla to make life even easier!

I must say I support the anti-microsoft movement, although some of the software they put out is usually viewed as essential. I am a huge advocate of thunderbird, and firefox of course. The Mozilla crew release some of the best open source based software there is, and its usually better than what MicroSift has to offer.